1. Field of the Invention
The present invention relates to a magnetic roller that is contained within a hollow non-magnetic body, i.e., a development sleeve, and which rotates relative to the hollow non-magnetic body, in order to convey a developer upon the hollow non-magnetic body to a latent image carrier, a developer carrier, i.e., a development roller, including the magnetic roller, a developing device including the developer carrier, a process cartridge including the developing device, and an image forming apparatus including the process cartridge.
2. Description of the Related Art
Typically, in an image forming apparatus of an electro-photographic system, an electrostatic latent image is formed that corresponds to image information upon a latent image carrier, which is formed from a photoconductive drum or a photoconductive belt, and thereafter, a developing operation is executed by way of a developing device upon the electrostatic latent image, and thereby a visible image is obtained.
In a developing process by way of the electro-photographic system thereupon, a developing system by way of a magnetic brush is widely used. When employing a two-component developer that is formed from a toner and a magnetic particle, with the developing system that is implemented by way of the magnetic brush, the magnetic brush is formed by causing the two-component developer to adhere magnetically to an external circumference of the developer carrier, and the development is performed upon a development region, i.e., a region whereupon an electrical field whereupon an image development is possible is maintained between a developer carrier and a latent image carrier, by causing the toner to be supplied and applied selectively to the latent image upon the latent image carrier that is positioned opposite to the magnetic brush, by way of an electrical field that is present between the latent image carrier whereupon the electrostatic latent image is formed, and a sleeve whereupon an electrical bias is impressed.
In recent years, an interest has arisen with regard to miniaturizing the developing device, and a necessity has commensurately arisen for miniaturizing a developing roller thereupon. It is difficult however, in practical terms, to achieve a strong magnetism characteristic of a primary pole portion of the development roller, which is typically not less than 100 millitesla (mT) upon the development roller, as well as a high precision thereof, however, with a material, a roller configuration, and a manufacturing method thereof, that has been conventionally employed therewith.
It is difficult to satisfy the requirement thereof with a ferrite class of magnet that is typically conventionally employed as a magnetic material therewith, and thus, a necessity has arisen for employing a rare earth magnet, such as a neodymium-iron-boron (NeFeB) magnet, upon the primary pole portion of the development roller thereof. The rare earth magnet is expensive, and thus, as a practical configuration of the development roller, i.e., a magnetic roller, a configuration would be desirable that employs the rare earth magnet only upon the primary pole portion, a high magnetism characteristic is required, and to use the ferrite type of magnet upon another pole thereof. More specifically, it would be possible to minimize a cost thereof in terms of the manufacturing method of the developing device by combining a rare earth magnetic block, which is configured of the rare earth magnet only upon the primary pole component of the roller, upon a magnetic roller that includes a depression part for a positioning thereupon of the rare earth magnetic block.
In addition, it would be possible to ensure a magnetic force aside from the primary development pole, even with a small magnetic roller, by treating a configuration of a small diameter magnetic roller as a magnetic roller, an axis whereof is integrated thereupon, and maintaining a magnetic volume thereof. A necessity arises thereupon, however, for setting a depth of the depression for positioning the rare earth magnetic block more deeply than a location of a support part thereupon, varying as a diameter of the magnetic roller thereof. Presuming such a structure for the magnetic roller involves a reduction of a size of the depression of the magnetic roller when forming the magnetic roller, resulting in an increased weakness in the support part of the magnetic roller, which may in turn lead to a fracturing of the support part of the magnetic roller either immediately after a formation thereof, when the magnetic roller is assembled and mounted, or when the magnetic roller is actually used. In order to prevent such a fracturing of the support part of the magnetic roller thereupon, a magnetic roller has been proposed that causes the support part of the magnetic roller to incorporate a curvature thereupon, as well as to narrow, in a staged manner, a diameter of the support part of the magnetic roller, starting from a diameter of a trunk portion of the magnetic roller proper; refer to Japanese Patent Application Laid Open No. 2000-114031 for particulars.
FIG. 8 is a front view of a conventional magnetic roller, and FIG. 9 is a diagram depicting a state wherein a resin is fully loaded into a casting mold with respect to a manufacturing of the conventional magnetic roller thereof. With regard to the casting mold of the magnetic roller that forms the conventional magnetic roller thereupon, a component that forms a support part, which includes a curvature upon the depression part thereof, results in an edge, which interferes with the resin being loaded into the casting mold, such as is depicted in FIG. 9. As a consequence thereof, a magnetic roller results that does not include the curvature upon the depression part thereof, or, put another way, a magnetic roller results that includes a component that is in a state wherein the resin is not completely loaded, such as is depicted in FIG. 8. As a consequence thereof, a problem arises, in a manner similar to the conventional magnetic roller thereof, wherein a fracture of the support part thereof occurs as a result of an impact of such as when the shrinkage or the imposition arises upon a joint of the support part and the depression part, which is formed upon a main body portion, with respect to the magnetic roller thereof. In addition, a problem also arises wherein a structure of a casting mold becomes increasingly complicated in order to cause the support part thereof to incorporate the curvature thereupon.
Furthermore, a magnetic roller has been proposed wherein the support part and the primary pole portion is formed in an integrated manner from a hard resinate magnetic material, in order to maintain the magnetic force of the primary pole portion, and another portion of the roller is formed from a soft resinate magnetic material comprising a “C” shape as viewed in a cross-section; refer to Japanese Patent Application Laid Open No. H11-242391 for particulars. When presuming such a configuration of the magnetic roller thereof, however, a problem arises wherein it becomes difficult to maintain the magnetic force upon other than the primary pole portion, as well as wherein the magnetic force or a half value width of the primary pole portion increases to a greater level than is necessary thereupon.